A closure package for closing off a damper tube simultaneously serves for the leadthrough of the piston rod, which is connected within the damper tube to a working piston of the vibration damper. The piston rod is guided by way of a guide bushing, and depending on the operating situation of the vibration damper, transverse forces may act on the piston rod, which transverse forces must be accommodated by the guide bushing. The damper tube is filled with a damping fluid, such that the closure package must furthermore perform the task of closing off the damper tube in liquid-tight fashion. Here, there is the problem in particular that the seal unit must be designed such that a pressure-tight closure of the damper tube is produced despite the piston rod led through the opening in the main body. Owing to the tasks that the closure package must perform, the latter is often also referred to as sealing and guiding pack.
DE 10 2007 005 690 A1 presents, for example, a closure package for closing off a damper tube of a vibration damper, and a guide bushing serves for guiding the piston rod which is inserted in a guide part of the closure package. Said document also presents a seal unit which is accommodated in a carrier part of the closure package. The main body of the closure package is thus of two-part form, necessitating a cumbersome design of the closure package.
FIG. 1 shows a cross-sectional view of a closure package 1 according to further general prior art, and the closure package 1 is held at the end side in a damper tube 10. As a main constituent of the closure package 1, the figure shows a main body 11, and in order for the main body 11 to be received in retained fashion in the damper tube 10, said main body has a circumferential groove 20 into which a pressed-in region 21 of the damper tube 10 is pressed owing to plastic deformation for example as a result of an external circumferential rolling process. This gives rise to a mechanically loadable, durable arrangement of the main body 11 in the damper tube 10. Furthermore, an O-ring seal 22 is provided between the main body 11 and the inner side of the damper tube 10, by means of which O-ring seal the interior, which is filled with damping liquid, of the damper tube 10 is closed off in pressure-tight fashion.
The piston rod 12 is guided in an axial direction 19 by way of a guide bushing 13 inserted in an opening in the main body 11, such that the piston rod 12 can perform a stroke movement in the damper tube 10. Here, the guide bushing 13 also accommodates forces acting laterally with respect to the axial direction 19. For a retained arrangement of the guide bushing 13, the latter is pressed into the opening in the main body 11, wherein permanent, secure seating of the guide bushing 13 is no longer necessarily ensured after a relatively long period of operation of the vibration damper. Depending on temperature influences and the expansion behavior of the materials involved in the event of a temperature change, the interference fit of the guide bushing 13 in the opening in the main body 11 may loosen, such that the guide bushing 13 can slip out of the opening in the main body 11 and thus be lost, resulting in total failure of the vibration damper.
Shown below the guide bushing 13 is a seal unit 14, 15, and the seal unit 14, 15 has a rod sealing element 14 and an outer sealing element 15. The rod sealing element 14 serves for contigious sealing against the piston rod 11, and annularly surrounds the latter. The outer sealing element 15 serves for the support of the rod sealing element 14, wherein the seal unit 14, 15 is held in the main body 11 of the closure package 1 by way of a closure plate 18. The closure plate 18 is in this case pressed into the receiving seat 23 in the main body 11.
The rod sealing element 14 bears, at the top side, against a sealing contact surface 11a in the main body 11. In the radially inner region of the rod sealing element 14, the lower end 13a of the guide bushing 13 comes into contact with the rod sealing element 14, and during the operation of the vibration damper, the stroke movement of the piston rod 12 along the axial direction 19 gives rise to a permanent movement of the rod sealing element 14 against the lower end 13a of the guide bushing 13. This can result in permanent damage to the rod sealing element 14, resulting in increased extrusion behavior of the pressure-loaded rod sealing element 14, and a further result is intense wear of and local damage to the surface of the rod sealing element 14. The slightly beveled lower end 13a of the guide bushing 13 is necessary, as the bevel constitutes an installation aid; furthermore, the internal bevel is required in order to improve the guidance of the piston rod 12. The intense load on the rod sealing element 14 can result in premature failure of the seal unit 14, 15, which constitutes a further disadvantage of the illustrated closure package 1 aside from the insecure arrangement of the guide bushing 13 in the main body 11.
Accordingly there is a need for a closure package for closing off a damper tube of a vibration damper that provides for an improved operational reliability and a longer service life for the vibration damper.